Water-Resources Investigations Report 78-29

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Abstract

The Tampa Reservoir Dam, constructed in 1945 on the lower Hillsborough River 10 miles above the mouth, provides 12.5 miles of natural channel storage for city water supply. Flow of the lower Hillsborough River and storage in Tampa Reservoir become deficient during annual dry periods. Excluding dead storage, Tampa Reservoir capacity is 2,000 million gallons at a maximum stage of 22.5 feet above mean sea level. For 20-year, annual-minimum-flow conditions, Hillsborough River flow is exceeded when the draft rate reaches 38 million gallons per day. In any year, at full capacity, Tampa Reservoir and Hillsborough River have a 5-percent chance of failing to supply at least 66 million gallons of water per day; and a 2-percent chance of failing to supply at least 59 million gallons per day. Runoff and effluent from agricultural, industrial, and urban areas enter the stream system above Tampa Reservoir. A wide range of chemical constituents, including nutrients, metals, herbicides, and pesticides analyzed in samples taken at the reservoir, are all below the maximum acceptable limits set by the U.S. Environmental Protection Agency for raw waters used for public supply. Water color exceeds the recommended level based on aesthetic considerations. The color is successfully removed through the treatment process at the Tampa water treatment plant. (Woodard-USGS)